1. Field of the Invention
The present invention is generally related to nuclear system pressurizers and in particular to the heater sleeves in the pressurizers.
2. General Background
The pressurizer in a nuclear reactor coolant system establishes and maintains the reactor coolant system pressure within the prescribed limits of the system. It provides a steam surge chamber and a water reserve to accommodate reactor coolant density changes during operation. A typical pressurizer is a vertical, cylindrical vessel with replaceable electric heaters in its lower section. The electric heaters are positioned below the normal water line and are actuated to restore normal operating pressure when the pressure in the reactor coolant system has decreased.
The electric heaters are comprised of a plurality of heating elements that extend through nozzles or sleeves through the wall of the pressurizer. Support plates inside the pressurizer are provided with holes in coaxial alignment with the holes in the pressurizer wall and the nozzles for receiving and supporting the heating elements. The nozzles extend outward from the pressurizer to provide exterior support to the heating elements. Due to the operating environment, it is a common requirement that heating elements and the nozzles through which they extend be replaced. Because alignment between the support plate holes and the nozzle is critical, it has previously been required that the replacement nozzle be fabricated to original design dimensional specifications and installed into the original bore in the pressurizer wall to insure proper alignment of the nozzle inner diameter with the corresponding support plate hole after welding. This process required that the removal of the original nozzle weld and installation of the repair weld be performed from inside the pressurizer because the bore through the pressurizer could not be enlarged for tooling access without potentially altering the alignment of the heater penetration with respect to the holes in the support plates. Since pressurizer components in nuclear power plants become radioactive after they have been in operation, performing such work inside the pressurizer is difficult and hazardous to personnel and thus impractical. What is needed is a means of replacing the heating element and nozzle without the need for personnel to enter a radioactive pressurizer.